(CNN) - A two-term Republican congressman and rising star in the GOP announced Monday that he's running in a special election this year for the U.S. Senate seat in Oklahoma that's opening up due to Sen. Tom Coburn's retirement.
The move by Rep. James Lankford follows by a day the announcements from two other Oklahoma Republicans that they would not be making Senate bids.
"After a great deal of thought, prayer and discussion with my family, I feel led to continue my Oklahoma common sense and principled approach to attack the deep problems in the United States Senate," said Lankford, according to excerpts released by his campaign.
"I am willing to wage a hard-fought campaign for the opportunity to continue Dr. Coburn's conservative legacy. I humbly ask for your vote in the primary election on June 24th and your support by joining our campaign team," Lankford added.
Coburn announced Thursday that he will retire at the end of the current congressional session, ending his second six-year term two years early. The 65-year old Republican Senator has been battling cancer, but said in a statement that his decision to step down at the end of this year "isn't about my health, my prognosis, or even by hopes and desires."
Oklahoma Gov. Mary Fallin's office said Friday that a special election will be scheduled to coincide with this year's midterm elections. The decision means potential candidates must file by April, setting the stage for a June primary fight, and, if necessary, an August runoff. The winner of the special general election in November will serve the final two years of Coburn's Senate term.
Lankford, first elected to Congress in 2010, has soared to the chairmanship of the Republican Policy Committee, the fifth ranked leadership post among House Republicans. He represents the state's fifth congressional district, which includes Oklahoma City. While Lankford's considered a solid conservative, the D.C.-based Senate Conservatives Fund said Monday that it won't support his Senate bid "because of his past votes to increase the debt limit, raise taxes, and fund Obamacare.
"We have reviewed his record and it's clear that conservatives cannot count on him to fight for their principles," added Matt Hoskins, the group's executive director.
Another conservative group, the Madison Project, also announced Monday that it wouldn't endorse Lankford.
Sunday, six-term GOP Rep. Tom Cole of Oklahoma announced he wouldn't run for the open Senate seat, saying he could do more good for the state in the House.
"My role as a Deputy Whip in the Republican Conference makes me much more valuable to Oklahoma and the Fourth District in the House than I could be as a freshman U.S. Senator," said Cole.
Oklahoma attorney General Scott Pruitt, a former state senator who launched a failed bid for Oklahoma's lieutenant governor slot in 2006, also took said he wouldn't run for the Senate seat, citing similar reasons as Cole.
"At present, my choice is clear," Pruitt said in a statement posted on his Facebook page. "It is serving as Oklahoma's Attorney General, where I can continue to lead the fight for the preservation of our freedoms and constitutional system."
Oklahoma House Speaker T.W. Shannon, an African-American who's also considered a rising star in the GOP, is mulling a Senate bid, as it Rep. Jim Bridenstine.
With Oklahoma considered a firmly red state, the winner of the GOP primary will be considered the favorite to win November's special election. The state's other U.S. Senator, Republican James Inhofe, as well as Fallin, the state's GOP governor, are both up for re-election in November.